Nuka or Scar. Scar, simply because he didn't even try to cover his own back, he needed others to do it for him. Instead of challenging Mufasa himself, like a real lion, he just devised a plan and when Simba returned he tried to run away and escape blame by putting it on the hyenas. And Nuka is just completely neurotic!

I'm not sure about the hyenas. I mean, they went after Scar to help him when he was cornered by Simba--they only backed off when Scar blamed them for everything. That was quite brave. I don't think they were cowards in any way.

Zazu often overreacts and gets really worried over everything, but he's just very sensible, so not a coward.

As for the others, they were all brave, no question and each of them showed it once at least.

nuka is not the worst character ever, banzai on the other hand is not the best character ever

This countdown is based on whose the BRAVEST character, not the best.

I do really think Scar, mostly for the reasons fireworks123 stated.